Add natspec for copied helpers

Author: stevieraykatz

src/L2/ReverseRegistrarV2.sol

@@ -264,13 +264,25 @@ contract ReverseRegistrarV2 is Ownable {
         }
     }
 
+    /// @notice Helper for converting an address stored as bytes into an address type.
+    ///
+    /// @dev Copied from ENS `AddrResolver`:
+    ///     https://github.com/ensdomains/ens-contracts/blob/staging/contracts/resolvers/profiles/AddrResolver.sol
+    ///
+    /// @param b Address bytes.
     function _bytesToAddress(bytes memory b) internal pure returns (address payable a) {
         require(b.length == 20);
         assembly {
             a := div(mload(add(b, 32)), exp(256, 12))
         }
     }
 
+    /// @notice Helper for converting an address into a bytes object.
+    ///
+    /// @dev Copied from ENS `AddrResolver`:
+    ///     https://github.com/ensdomains/ens-contracts/blob/staging/contracts/resolvers/profiles/AddrResolver.sol
+    ///
+    /// @param a Address.
     function _addressToBytes(address a) internal pure returns (bytes memory b) {
         b = new bytes(20);
         assembly {